This invention relates to a method for preparing a therapeutic or diagnostic Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound by identifying a Nucleic Acid Ligand by SELEX methodology and associating the Nucleic Acid Ligand with a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound. The invention further relates to improving the pharmacokinetic properties of a Nucleic Acid Ligand by associating the Nucleic Acid Ligand to a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound to form a Complex. The invention further relates to a method for targeting a therapeutic or diagnostic agent to a specific predetermined biological Target by associating the agent with a Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound, wherein the Nucleic Acid Ligand has a SELEX Target associated with the specific predetermined Target and the Nucleic Acid Ligand is associated with the exterior of the Complex. The invention also includes complexes comprising one or more Nucleic Acid Ligand in association with a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound.
A. SELEX
The dogma for many years was that nucleic acids had primarily an informational role. Through a method known as Systematic Evolution of Ligands by EXponential enrichment, termed SELEX, it has become clear that nucleic acids have three dimensional structural diversity not unlike proteins. SELEX is a method for the in vitro evolution of nucleic acid molecules with highly specific binding to target molecules and is described in U.S. patent application Ser. No. 07/536,428, filed Jun. 11, 1990, entitled xe2x80x9cSystematic Evolution of Ligands by Exponential Enrichmentxe2x80x9d, now abandoned, U.S. patent application Ser. No. 07/714,131, filed Jun. 10, 1991, entitled xe2x80x9cNucleic Acid Ligandsxe2x80x9d, now U.S. Pat. No. 5,475,096, U.S. patent application Ser. No. 07/931,473, filed Aug. 17, 1992, entitled xe2x80x9cNucleic Acid Ligandsxe2x80x9d, now U.S. Pat. No. 5,270,163 (see also PCTIUS91/04078), each of which is specifically incorporated by reference herein. Each of these applications, collectively referred to herein as the SELEX Patent Applications, describes a fundamentally novel method for making a Nucleic Acid Ligand to any desired target molecule. The SELEX process provides a class of products which are referred to as Nucleic Acid Ligands, each ligand having a unique sequence, and which has the property of binding specifically to a desired target compound or molecule. Each SELEX-identified Nucleic Acid Ligand is a specific ligand of a given target compound or molecule. SELEX is based on the unique insight that Nucleic Acids have sufficient capacity for forming a variety of two- and three-dimensional structures and sufficient chemical versatility available within their monomers to act as ligands (form specific binding pairs) with virtually any chemical compound, whether monomeric or polymeric. Molecules of any size or composition can serve as targets.
The SELEX method involves selection from a mixture of candidate oligonucleotides and step-wise iterations of binding, partitioning and amplification, using the same general selection scheme, to achieve virtually any desired criterion of binding affinity and selectivity. Starting from a mixture of Nucleic Acids, preferably comprising a segment of randomized sequence, the SELEX method includes steps of contacting the mixture with the target under conditions favorable for binding, partitioning unbound Nucleic Acids from those Nucleic Acids which have bound specifically to target molecules, dissociating the Nucleic Acid-target complexes, amplifying the Nucleic Acids dissociated from the Nucleic Acid-target complexes to yield a ligand-enriched mixture of Nucleic Acids, then reiterating the steps of binding, partitioning, dissociating and amplifying through as many cycles as desired to yield highly specific high affinity Nucleic Acid Ligands to the target molecule.
It has been recognized by the present inventors that the SELEX method demonstrates that Nucleic Acids as chemical compounds can form a wide array of shapes, sizes and configurations, and are capable of a far broader repertoire of binding and other functions than those displayed by Nucleic Acids in biological systems.
The present inventors have recognized that SELEX or SELEX-like processes could be used to identify Nucleic Acids which can facilitate any chosen reaction in a manner similar to that in which Nucleic Acid Ligands can be identified for any given target. In theory, within a Candidate Mixture of approximately 1013 to 1018 Nucleic Acids, the present inventors postulate that at least one Nucleic Acid exists with the appropriate shape to facilitate each of a broad variety of physical and chemical interactions.
The basic SELEX method has been modified to achieve a number of specific objectives. For example, U.S. patent application Ser. No. 07/960,093, filed Oct. 14, 1992, entitled xe2x80x9cMethod for Selecting Nucleic Acids on the Basis of Structure.xe2x80x9d describes the use of SELEX in conjunction with gel electrophoresis to select Nucleic Acid molecules with specific structural characteristics, such as bent DNA. U.S. patent application Ser. No. 08/123,935, filed Sep. 17, 1993, entitled xe2x80x9cPhotoselection of Nucleic Acid Ligands,xe2x80x9d describes a SELEX based method for selecting Nucleic Acid Ligands containing photoreactive groups capable of binding and/or photocrosslinking to and/or photoinactivating a target molecule. U.S. patent application Ser. No. 08/134,028, filed Oct. 7, 1993, entitled xe2x80x9cHigh-Affinity Nucleic Acid Ligands That Discriminate Between Theophylline and Caffeine,xe2x80x9d describes a method for identifying highly specific Nucleic Acid Ligands able to discriminate between closely related molecules, which can be non-peptidic, termed Counter-SELEX. U.S. patent application Ser. No. 08/143,564, filed Oct. 25, 1993, entitled xe2x80x9cSystematic Evolution of Ligands by EXponential Enrichment: Solution SELEX,xe2x80x9d describes a SELEX-based method which achieves highly efficient partitioning between oligonucleotides having high and low affinity for a target molecule.
The SELEX method encompasses the identification of high-affinity Nucleic Acid Ligands containing modified nucleotides conferring improved characteristics on the ligand, such as improved in vivo stability or improved delivery characteristics. Examples of such modifications include chemical substitutions at the ribose and/or phosphate and/or base positions. SELEX-identified Nucleic Acid Ligands containing modified nucleotides are described in U.S. patent application Ser. No. 08/117,991, filed Sep. 8, 1993, entitled xe2x80x9cHigh Affinity Nucleic Acid Ligands Containing Modified Nucleotides,xe2x80x9d that describes oligonucleotides containing nucleotide derivatives chemically modified at the 5- and 2xe2x80x2-positions of pyrimidines. U.S. patent application Ser. No. 08/134,028, supra, describes highly specific Nucleic Acid Ligands containing one or more nucleotides modified with 2xe2x80x2-amino (2xe2x80x2-NH2), 2xe2x80x2-fluoro (2xe2x80x2-F), and/or 2xe2x80x2-O-methyl (2xe2x80x2-OMe). U.S. patent application Ser. No. 08/264,029, filed Jun. 22, 1994, entitled xe2x80x9cNovel Method of Preparation of 2xe2x80x2 Modified Pyrimidine Intramolecular Nucleophilic Displacementxe2x80x9d, describes oligonucleotides containing various 2xe2x80x2-modified pyrimidines.
The SELEX method encompasses combining selected oligonucleotides with other selected oligonucleotides and non-oligonucleotide functional units as described in U.S. patent application Ser. No. 08/284,063, filed Aug. 2, 1994, entitled xe2x80x9cSystematic Evolution of Ligands by Exponential Enrichment: Chimeric SELEXxe2x80x9d and U.S. patent application Ser. No. 08/234,997, filed Apr. 28, 1994, entitled xe2x80x9cSystematic Evolution of Ligands by Exponential Enrichment: Blended SELEX,xe2x80x9d respectively. These applications allow the combination of the broad array of shapes and other properties, and the efficient amplification and replication properties, of oligonucleotides with the desirable properties of other molecules. Each of the above described patent applications which describe modifications of the basic SELEX procedure are specifically incorporated by reference herein in their entirety.
B. Lipid Constructs
Lipid Bilayer Vesicles are closed, fluid-filled microscopic spheres which are formed principally from individual molecules having polar (hydrophilic) and non-polar (lipophilic) portions. The hydrophilic portions may comprise phosphate, glycerylphosphato, carboxy, sulfato, amino, hydroxy, choline or other polar groups. Examples of lipophilic groups are saturated or unsaturated hydrocarbons such as alkyl, alkenyl or other lipid groups. Sterols (e.g., cholesterol) and other pharmaceutically acceptable adjuvants (including anti-oxidants like alpha-tocopherol) may also be included to improve vesicle stability or confer other desirable characteristics.
Liposomes are a subset of these bilayer vesicles and are comprised principally of phospholipid molecules that contain two hydrophobic tails consisting of fatty acid chains. Upon exposure to water, these molecules spontaneously align to form spherical, bilayer membranes with the lipophilic ends of the molecules in each layer associated in the center of the membrane and the opposing polar ends forming the respective inner and outer surface of the bilayer membrane(s). Thus, each side of the membrane presents a hydrophilic surface while the interior of the membrane comprises a lipophilic medium. These membranes may be arranged in a series of concentric, spherical membranes separated by thin strata of water, in a manner not dissimilar to the layers of an onion, around an internal aqueous space. These multilamellar vesicles (MLV) can be converted into small or Unilamellar Vesicles (UV), with the application of a shearing force.
The therapeutic use of jiposomes includes the delivery of drugs which are normally toxic in the free form. In the liposomal form, the toxic drug is occluded, and may be directed away from the tissues sensitive to the drug and targeted to selected areas. Liposomes can also be used therapeutically to release drugs over a prolonged period of time, reducing the frequency of administration. In addition, liposomes can provide a method for forming aqueous dispersions of hydrophobic or amphiphilic drugs, which are normally unsuitable for intravenous delivery.
In order for many drugs and imaging agents to have therapeutic or diagnostic potential, it is necessary for them to be delivered to the proper location in the body, and the liposome can thus be readily injected and form the basis for sustained release and drug delivery to specific cell types, or parts of the body. Several techniques can be employed to use liposomes to target encapsulated drugs to selected host tissues, and away from sensitive tissues. These techniques include manipulating the size of the liposomes, their net surface charge, and their route of administration. MLVs, primarily because they are relatively large, are usually rapidly taken up by the reticuloendothelial system (principally the liver and spleen). UVs, on the other hand, have been found to exhibit increased circulation times, decreased clearance rates and greater biodistribution relative to MLVs.
Passive delivery of liposomes involves the use of various routes of administration, e.g., intravenous, subcutaneous, intramuscular and topical. Each route produces differences in localization of the liposomes. Two common methods used to direct liposomes actively to selected target areas involve attachment of either antibodies or specific receptor ligands to the surface of the liposomes. Antibodies are known to have a high specificity for their corresponding antigen and have been attached to the surface of liposomes, but the results have been less than successful in many instances. Some efforts, however, have been successful in targeting liposomes to tumors without the use of antibodies, see, for example, U.S. Pat. No. 5,019,369.
An area of development aggressively pursued by researchers is the delivery of agents not only to a specific cell type but into the cell""s cytoplasm and, further yet, into the nucleus. This is particularly important for the delivery of biological agents such as DNA, RNA, ribozymes and proteins. A promising therapeutic pursuit in this area involves the use of antisense DNA and RNA oligonucleotides for the treatment of disease. However, one major problem encountered in the effective application of antisense technology is that oligonucleotides in their phosphodiester form are quickly degraded in body fluids and by intracellular and extracellular enzymes, such as endonucleases and exonucleases, before the target cell is reached. Intravenous administration also results in rapid clearance from the bloodstream by the kidney, and uptake is insufficient to produce an effective intracellular drug concentration. Liposome encapsulation protects the oligonucleotides from the degradative enzymes, increases the circulation half-life and increases uptake efficiency as a result of phagocytosis of the Liposomes. In this way, oligonucleotides are able to reach their desired target and to be delivered to cells in vivo.
A few instances have been reported where researchers have attached antisense oligonucleotides to Lipophilic Compounds or Non-Immunogenic, High Molecular Weight Compounds. Antisense oligonucleotides, however, are only effective as intracellular agents. Antisense oligodeoxyribonucleotides targeted to the epidermal growth factor (EGF) receptor have been encapsulated into Liposomes linked to folate via a polyethylene glycol spacer (folate-PEG-Liposomes) and delivered into cultured KB cells via folate receptor-mediated endocytosis (Wang et al. (1995) 92:3318-3322). In addition, a Lipophilic Compound covalently attached to an antisense oligonucleotide has been demonstrated in the literature (EP 462 145 B1).
The present invention provides a method for preparing a therapeutic or diagnostic Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound by the method comprising identifying a Nucleic Acid Ligand from a Candidate Mixture of Nucleic Acids where the Nucleic Acid is a ligand of a given target by the method of (a) contacting the Candidate Mixture of Nucleic Acids with the target, (b) partitioning between members of said Candidate Mixture on the basis of affinity to the target, and c) amplifying the selected molecules to yield a mixture of Nucleic Acids enriched for Nucleic Acid sequences with a relatively higher affinity for binding to the target, and associating said identified Nucleic Acid Ligand with a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound.
In another embodiment, this invention provides a method for improving the cellular uptake of a Nucleic Acid Ligand having an intracellular SELEX Target by associating the Nucleic Acid Ligand with a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound to form a Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound and administering the Complex to a patient.
In another embodiment, this invention provides a method for improving the pharmacokinetic properties of a Nucleic Acid Ligand by associating the Nucleic Acid Ligand to a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound to form a Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or a Non-Immunogenic, High Molecular Weight Compound and administering the Complex to a patient.
In another embodiment, this invention provides a method for targeting a therapeutic or diagnostic agent to a specific predetermined biological Target in a patient comprising associating the therapeutic or diagnostic agent with a Complex comprised of a Nucleic Acid Ligand and a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound, wherein the Nucleic Acid Ligand has a SELEX Target associated with the specific predetermined Target, and the Nucleic Acid Ligand is associated with the exterior of the Complex and administering the Complex to a patient.
It is an object of the present invention to provide Complexes comprising one or more Nucleic Acid Ligands in association with a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound and methods for producing the same. It is a further object of the invention to provide one or more Nucleic Acid Ligands in association with a Lipophilic Compound or Non-Immunogenic, High Molecular Weight Compound with Improved Pharmacokinetic Properties. In another aspect of the invention, the Lipophilic Compound is a Lipid Construct. In this embodiment, the Lipid Construct is preferably a Lipid Bilayer Vesicle and most preferably a Liposome. In certain embodiments of the invention the Lipophilic Compound is cholesterol, dialkyl glycerol, or diacyl glycerol. In another embodiment of the invention, the Non-Immunogenic, High Molecular Weight Compound is PEG. In another embodiment of the invention, the Non-Immunogenic, High Molecular Weight Compound is magnetite. In the preferred embodiment, the Nucleic Acid Ligand is identified according to the SELEX method.
In embodiments of the invention directed to Complexes comprising cholesterol, dialkyl glycerol, diacyl glycerol, PEG, or magnetite in association with a Nucleic Acid Ligand or ligands, the Nucleic Acid Ligand or ligands can serve in a targeting capacity.
In embodiments of the invention directed to Complexes comprising a Lipid Construct where the Lipid Construct is of a type that has a membrane defining an interior compartment such as a Lipid Bilayer Vesicle, the Nucleic Acid Ligand in association with the Lipid Construct may be associated with the membrane of the Lipid Construct or encapsulated within the compartment. In embodiments where the Nucleic Acid Ligand is in association with the membrane, the Nucleic Acid Ligand can associate with the interior-facing or exterior-facing part of the membrane, such that the Nucleic Acid Ligand is projecting in to or out of the vesicle. In embodiments where the Nucleic Acid Ligand is projecting out of the Complex. the Nucleic Acid Ligand can serve in a targeting capacity Non-Immunogenic, High Molecular Weight Compounds can also be associated with the membrane. In one embodiment, the Nucleic Acid Ligand may be associated with a Non-Immunogenic, High Molecular Weight Compound which is associated with the membrane. The membrane may have associated with it additional Non-Immunogenic, High Molecular Weight Compounds not associated with a Nucleic Acid Ligand.
In embodiments where the Nucleic Acid Ligand of the Complex serves in a targeting capacity, the Complex can incorporate or have associated with it therapeutic or diagnostic agents. In one embodiment, the therapeutic agent is a drug. In an alternative embodiment, the therapeutic or diagnostic agent is one or more additional Nucleic Acid Ligands. Nucleic Acid Ligands specific for different targets can project from the external surface of the Complex. The Complex can project from the external surface one or more Nucleic Acid Ligands which are specific for different SELEX Targets on the same Target.
These and other objects, as well as the nature, scope and utilization of this invention, will become readily apparent to those skilled in the art from the following description and the appended claims.